The magnetic disk medium of the vertical magnetic memory system is used in a composite magnetic head having a TMR (tunnel magneto-resistance) head or a GMR (giant magneto-resistance) head, which is a memory medium separable from the head by 10 nanometer or less controllably.
Such magnetic disk medium generally includes a glass substrate, a soft magnetic layer formed on the glass substrate and a magnetic layer provided on the soft magnetic layer. Discrete tracks are formed in a discrete substrate by etching the magnetic layer. (Incidentally, the term “disk substrate” is used as a material of a magnetic disk to be mounted on a hard disk.)
The etching for forming grooves between tracks is performed through an uneven photo-resist film. The unevenness of the photo-resist film is formed by using the nano-print lithography and pushing the photo-resist film with an uneven stamper. The track width of the discrete track formed by the dry etching through the uneven photo-resist is 100 nm or less and the groove separating adjacent tracks is filled with a non-magnetic material in a later step. Such kind of the technique is described in JP-2007-012119A and JP-2007-149155A, etc.
In this vertical magnetic recording medium, a data area and a servo area are separated and a servo information for a track positioning of the magnetic head area and a track number, etc., are provided. In the original disk which becomes an unevenness stamper, unevenness for forming a servo area is provided, the data area and the servo area are formed in the disk medium and the servo information, etc., are set. Such kind of test technique is described in, for example, JP-2008-176835A and is well known.
The test of the data area in such kind of vertical magnetic recording medium is performed by recording of bit signal data, in which “010101 . . . ”, for example, is repeated, and reading the data. Since a level of the read signal is changed correspondingly to a change point of the changing magnetization from “0” to “1” or “1” to “0” in such test, there are jitter noise test for testing transition position of a regeneration waveform signal corresponding to the change point of magnetization similarly to the conventional horizontal recording disk test and the T50 noise test for performing a test for regeneration waveform width in ±50% level, etc. The technique of such kind is described in JP-2008-171507A and is well known.
FIG. 7 shows about one fourth of a DTM 1 to be tested.
In the DTM 1, servo area 1a corresponding to respective sectors. In the servo area 1a, a track number, servo information (servo burst signal) for positioning ON track positioning and sector number are recorded. After the servo areas, a data area 1e in which respective discrete track 1b is provided is formed. Each of non-magnetic members 1c is provided between adjacent discrete tracks 1b. 
The servo area 1a and the data area 1e are provided in each sector and the number of sectors is usually about 256 for one track.
Incidentally, FIG. 7 shows an enlarged schematic depiction of the servo area 1a and the data area for the purpose of description.
A DTM is currently paid attention as a technique capable of realizing ultra high density recording exceeding 1 terabit/(inch)2 for 2.5 inches several years later. Further, the bit patterned medium (BPM) having discrete tracks, which are finely separated magnetically in the track direction, has been entered into the practical implementation step recently.
However, since the information of the servo area is not the repeating bit pattern such as “010101 . . . ” of the data area, it is difficult to apply the electric test in the data area of such as the jitter noise test, etc., to the servo area for the reason that change of the bit density of a read signal influences when a relative comparison is performed by setting a constant slice level. Therefore, it is usual to perform the test of whether or not a servo area is formed in the DTM correctly with respect to the original disk by a video test, etc., by an optical photographing.
However, in such video test, the load of image processing of the data processing device becomes higher and the throughput of the test processing becomes lower when the recording density becomes higher.